Innumerable lives have been lost to hemorrhage, escape of tissue fluids from burned or denuded body surfaces, and infections or toxic effects consequent to contamination of open wounds. Accordingly, a variety of methods have been used to stop or control losses of blood or fluids and imitate defensive functions of intact skin. Heavy bleeding may be controlled in many cases if large vessels can be flattened. This may be done by transfer of external pressure through adjacent tissue or bandaging material. If less severe injuries require surgical care, “first aid strips” or similar non-adhesive bandages may limit minor hemorrhage and prevent wound contamination.
Unfortunately, severe injuries and burns often exceed the capabilities of first aid bandages. Some injuries exceed the capabilities of all bandages and care available at the site of injury. Victims frequently bleed to death before they can benefit from care by highly trained and superbly equipped surgeons who might save them. It is known that hemorrhage is the cause of many battlefield deaths and increases the morbidity of surviving casualties. An effective method for controlling hemorrhage in forward treatment elements (pre-hospital, non-physician providers) would greatly reduce combat mortality rates and decrease logistical requirements for combat casualty care. To meet U.S. Army requirements, “. . . a topical hemostatic agent must control rapidly flowing, otherwise lethal, large venous or arterial hemorrhage, through a pool of blood—without vascular control.” Hemorrhage control poses similar life-threatening problems with non-military personnel.
Relatively minor injuries, such as a superficially cut finger or scraped knee, are often covered with sterile cotton gauze pads that are held over the injured site by pressure from an adhesive barrier strip affixed to adjacent normal skin. Such first aid strips may be used to sequester small amounts of blood within the absorbent pad until components of blood and damaged tissue can form a fibrin-based clot. The clot initially clogs the ends of small blood vessels and adheres to wounded surfaces. When large vessels are cut or torn, the rapid flow of escaping blood tends to remove fibrin clots before they can clog the vessel and adhere to the adjacent damaged tissue. There is a requirement for material able to arrest such major hemorrhage.
In many cases, blood adhering to damaged tissue is clotted and slowly transformed into a scab that serves as a skin substitute; it retains body fluids while sealing out bacteria and other environmental hazards. Wound healing normally takes place under cover of the protective scab, which prevents drying of underlying cells and undesirable inflammatory reactions that limit normal healing. Such healing requires closure of any void with fibroblasts and the migration of epidermal cells over fibroblasts and fibroblastic collagen products under physiological conditions. There is a need for methods able to rapidly provide the protective functions normally provided by epithelial cells and to foster re-epithelialization for re-establishment of such functions. An artificial scab is expected to provide such immediate protection but it may also be used to prevent or retard possibly disfiguring scar formation.
Military organizations have found it difficult to protect human skin against some chemical warfare agents. These include GB (isopropyl-methylphosphonofluridate), GD (1,2,2-trimethylpropyl methylphosphonofluridate) and VX (o-ethyl S-[2-(diisopropylamino)ethyl]methylphosphonothiolate), each an anticholinesterase “nerve agent”, vesicants such as HD (bis-2-chloroethyl sulfide) and its close relative that is known as sesquimustard, “tear gas” irritant/vesicants such as CS (o-chlorobenzylidene malononitrile) and CN (chloracetophenone), and various psychotomimietics such as BZ and EA3580 (anticholinergic agent prototypes). For instance, the need for skin protection against liquid mustard agents was recognized during World War I. Accordingly, several ointments or creams (topical skin protectants) were developed to shield skin from contamination with toxic chemical warfare agents. Some of these protectants incorporated detoxifying components, thickeners, and camouflage pigments (example: M-5 ointment).
There are similar problems in protecting normal skin from noxious chemicals and the sealing of wounded tissues from exposure to infection and drying. Many “protective cream” products have been made and sold for the purpose of limiting access of noxious chemicals to skin. However, most incorporate lipophilic substances that have proven ineffective against the lipophilic chemical warfare agents. Skin exposure reduction paste against chemical warfare agents (SERPACWA), a mixture of non-wettable fluorocarbon compounds, is the only material approved by the U.S. Army and the Federal Food and Drug Administration for such protection. However, current instructions for its use state, “Do not apply SERPACWA to open wounds or remove bandages to apply SERPACWA to those areas.” Further, many bum dressings and wound dressings provide protection for the damaged tissues, but none offer significant similarity to the properties of normal scabs that foster re-epithelialization.
There are a number of medical and non-medical applications that depend upon temporary adhesion between or to body surfaces. Some depend upon establishment of clean, dry surfaces. For example, first aid strips require such surfaces for attachment with a pressure-sensitive adhesive. Dental adhesives require a moist surface for attachment of dentures. Cyanoacrylate “tissue glues” react with very thin layers of water on normal skin or wounded tissue surfaces that can be placed in apposition. However, none of these adhesives is compatible with substantial amounts or depths of water or blood on a body surface. None are useful as soft tissue splints that stabilize torn tissue in the manner of bone fragment stabilization with splints.
Available adhesives lack hydrophilic properties optimal for product use as a vehicle for drugs to be absorbed from wounds, or on skin for retention of dermatological treatment substances intended to modify the stratum corneum. For instance, lipophilic adhesives and pharmaceutical vehicles adhere poorly to wet surfaces of wounds. They tend to retain lipophilic drugs (for example, vitamins A, D, and E that are known to promote wound healing) rather than facilitate their distribution into wounded tissue. In contrast, lipophilic materials readily tend to leave hydrophilic materials to enter lipophilic tissue membranes.